1. Field
Exemplary embodiments of the present invention relate to a semiconductor designing technology, and more particularly, to a clock generation circuit for generating an internal clock signal and a semiconductor memory device employing the clock generation circuit.
2. Description of the Related Art
Generally, semiconductor memory devices including a Double Data Rate Synchronous Dynamic Random Access Memory (DDR SDRAM) device receives an external clock signal and generates an internal clock signal, and performs diverse operations based on the generated internal clock signal. Therefore, the semiconductor memory devices may include an internal clock generation circuit for generating an internal clock signal.
Semiconductor memory devices are demanded to operate faster and faster, and this causes new phenomena such as electro-magnetic interference. The electro-magnetic interference usually occurs when a highly integrated circuit operates at a fast speed, and the electro-magnetic interference causes malfunction of a circuit. The Federal Communications Commission (FCC) provides restriction on the occurrence of the electro-magnetic interference, and semiconductor memory devices are designed in conformity with the recommended value prescribed by the FCC.
The electro-magnetic interference occurs as the length of an internal line becomes as short as the wavelength of an internal clock signal. The short internal line functions as an antenna and increases the radiation of electro-magnetic wave, eventually causing electro-magnetic interference. As semiconductor memory devices operate faster, while occupying smaller areas, the electro-magnetic interference may become worse and the circuit malfunction may be serious. Therefore, it may be desirable to develop a technology for getting rid of, or alleviating the electro-magnetic interference.